For the past 15 months, one subject has provoked more discussion, debate and disagreement among educationalists in Wales than any other: the Pisa (Programme for International Student Assessment) education rankings.
Pisa, run by the Organisation for Economic Cooperation and Development (OECD), has divided the education sector into those who think Wales's "disastrous" 2009 test results point to a national crisis and those who think that position is a gross exaggeration.
The backlash against the results - in which Wales performed worse than the other UK nations in reading, maths and science - has grown in recent months. And now the government has published a guide for teachers that is designed to show how they should incorporate Pisa into their lessons, prompting criticisms that ministers are encouraging schools to "game" the system.
The guidance builds on a pledge from education minister Leighton Andrews to integrate Pisa assessments into school assessment at age 15 to improve pupils' "life skills". The 50-page document aims to ensure that there is "an understanding in the educational community in Wales as to how Pisa assessments work in terms of contexts, demand and structure and how they can be used to support improved learning and teaching".
It contains sample questions and a series of tasks that teachers can use in the classroom.
The government is keen to avoid accusations that they are prepping pupils and teachers, and the document states on a number of occasions that "exposing learners to more Pisa-style assessment is not about 'practising' or 'teaching to the test'".
Rather, it is about "checking if learners understand how to access information and apply skills and knowledge".
But opponents, dubbed "flat-earthers" by some in government, have serious reservations.
Rex Phillips, Wales organiser for teaching union the NASUWT, accused the education minister of creating a "crisis" over Pisa and questioned whether the document would result in teaching to the test. "Our concern would be that this will lead to a narrowing of the curriculum and the curriculum being geared solely towards Pisa," he said. "Scoring well in Pisa is merely a badge for the government to wear - it's not for pupils."
But David Reynolds, professor of educational effectiveness at the University of Southampton and a senior policy adviser to the Welsh government, said that the importance of Pisa could not be over-emphasised. "It's about ensuring that Welsh pupils get the opportunity to show what they can do and familiarising them with this sort of external testing.
"The Welsh education system has been traditionally good at disseminating knowledge and we are moving towards a skills-based approach. Pisa is the next step: meta-cognitive thinking and advanced problem solving, which is not something we have been strong at in Wales.
"That will ultimately help to improve GCSE results and you will see across-the-board educational gains."
Mr Andrews has said that the Pisa tests are challenging because they take pupils out of their "comfort zones". By taking teachers out of theirs, he is hoping to push Wales into the top 20 of the rankings by 2015.
Out of the 67 countries that took part in the 2009 Pisa tests, Wales was ranked 38th for reading, 40th for maths and 30th for science.
In each category, Wales ranked lower than the three other UK countries and the OECD average, and recorded lower scores than in the 2006 tests.
Out of the 57 countries that took part in the 2006 Pisa tests, Wales was ranked 30th for reading, 34th for maths and 22nd for science.